In the aircraft industry in particular, equipment, such as electric and avionic equipment, is known to be connected mechanically to supporting structures, in particular honeycomb panels.
Such equipment is also connected electrically to the supporting structures, which are considered equipotential ground surfaces.
More specifically, the equipment is connected electrically to the supporting structures so that the electric contact resistance between them does not exceed 2.5 mΩ, as required by current regulations.
This protects people from electric discharges both on the ground and in flight, prevents the formation of fire-hazardous electric arcs, prevents the formation of electrostatic charges capable of causing interference, and ensures effective equipment insulation.
In the aircraft industry, the supporting structure is usually a honeycomb panel bounded on the top and bottom by two conducting metal, e.g. aluminium, sheets.
The metal sheets are normally coated with electrically insulating material.
The equipment is connected mechanically to the panel by a number of inserts.
More specifically, each insert substantially comprises a head housed loosely inside a through hole in the top sheet of the panel; and a stem housed loosely inside a seat in the panel.
The insert heads are connected to respective fastening portions of the equipment.
Known inserts therefore only provide for connecting the equipment mechanically to the supporting structure, and are insulated electrically from the supporting structure by there being no electric contact between conducting parts of the sheet and conducting parts of the inserts.
The equipment is connected electrically to the supporting structure by forming conducting areas on the top sheet of the panel, i.e. areas around respective anchoring portions of the equipment resting on the top sheet of the panel.
The conducting areas are formed by first removing the insulation coating from the areas of the top sheet surrounding the anchoring portions, and then protecting the areas with conductive corrosionproofing material.
Alternatively, outer surface areas of the sheet surrounding the anchoring portions may be left uncoated and protected with conductive corrosionproofing material.
Electric connection of the equipment to the supporting structure can therefore only be tested after the equipment is fixed to the insert and connected electrically to the sheet on the panel by the anchoring portions.
A need is felt within the industry to enable electric connection of the equipment to the supporting structure to be tested when fitting the insert.
In the case of equipment anchoring portions in the form of a flat surface resting on the top sheet, a large area of the insulation coating, equal to the area of the anchoring portions, must be removed from the top sheet.
Removing the insulation coating from the top sheet of the supporting structure also results in the formation of a step on the top sheet.
In the case of equipment anchoring portions in the form of a flat surface resting on the top sheet, the step formed may interrupt electric connection between the equipment and the supporting structure.
The above known solution therefore only ensures electric connection between the equipment and the supporting structure when the anchoring portions of the equipment are in the form of feet projecting from the underside surface of the equipment.
A need is felt within the industry to ensure electric conductivity of the mechanical connection between the equipment and supporting structure, and to reduce or even eliminate removal of the insulation coating from the supporting structure sheet, to enable easier, faster connection of the equipment to the supporting structure.